Heretofore, a method for manufacturing a three-dimensional shaped object by irradiating a powder material with a light beam has been known (such method can be generally referred to as “selective laser sintering method”). Such method can produce the three-dimensional shaped object by repeating the following steps (i) and (ii):
(i) forming a solidified layer by irradiating a predetermined portion of a powder layer with a light beam, thereby allowing a sintering of the predetermined portion of the powder or a melting and subsequent solidification thereof; and
(ii) forming another solidified layer by newly forming a powder layer on the resulting solidified layer, followed by similarly irradiating the powder layer with the light beam. See JP-T-01-502890 or JP-A-2000-73108, for example.
The three-dimensional shaped object thus obtained can be used as a metal mold in a case where inorganic powder material such as a metal powder and a ceramic powder is used as the powder material. While on the other hand, the three-dimensional shaped object can be used as a model or replica in a case where organic powder material such as a resin powder and a plastic powder is used as the powder material. This kind of technology makes it possible to produce the three-dimensional shaped object with a complicated contour shape in a short period of time.
By way of the case wherein the metal powder is used as the powder material, and the three-dimensional shaped object is used as the metal mold, the selective laser sintering method will be described. As shown in FIGS. 1A and 1B, a powder layer 22 with a predetermined thickness “t1” is firstly formed on a base plate 21 (see FIG. 1A) and then a predetermined portion of the powder layer 22 is irradiated with a light beam to form a solidified layer 24 (see FIG. 1B). Then, another powder layer 22 is newly provided on the solidified layer 24 thus formed, and is irradiated again with the light beam to form another solidified layer. In this way, the solidified layers are repeatedly formed, making it possible to produce a three-dimensional shaped object with a plurality of the solidified layers 24 stacked integrally. The lowermost solidified layer can be formed in a state of being adhered to the surface of the base plate. Therefore, the three-dimensional shaped object and the base plate are mutually integrated. The integrated “three-dimensional shaped object” and “base plate” can be used as the metal mold as they are.
The three-dimensional shaped object obtained by the laser-beam irradiation has a relatively roughened surface. In general, the shaped object has the roughened surface Rz of several hundred micrometers. This is attributed to the fact that the surface of the solidified layer has the adhered powder. When the solidified layer is formed, the energy of the laser beam is changed into heat, which causes the irradiated powder particles to melt. The melted powder particles are fused with each other during the subsequent cooling step thereof. In this regard, the temperature can rise in the surrounding powder region of the irradiated point, and thus such surrounding powder tends to adhere to the surface of the solidified layer. This adherence of the powder causes the roughened surface of the three-dimensional shaped object, and thereby a machining processing of the surface is necessary. Specifically, the surface of the obtained three-dimensional shaped object is wholly required to be subjected to a machining process.